You did not completely tear down/unwind the transformer, I would expect there to be one in the center. It likely just needed a few more seconds to trip since the whole mass has to heat up (one can see only the outer layer really got hot, the center windings don't have damaged insulation yet).

The thermal fuse is there more as a long term overload protection, not really appropruiate for this case although it's likely it would have tripped before things got melty enough to affect outside stuff (smoke is impressive, but it takes a lot more heat before there is a real risk of setting external stuff on fire).This really needs a fuse on the input. Pretty crazy, never seen a direct input in a long time even on the cheapest Chinese crap I have.

Seems unlikely. Generally its on the outer windings and the transformer would have some indication of one being inside (bump in the tape, or a label).

A dropped neutral in 120v countries is not an unforseen event. What did seem strange to me is that UL hasn't got a lot registered under this category, and what is are mostly soldering guns and firesticks. There is a Snap-On transformer based station. But maybe they just don't do a lot of soldering station work.I don't remember seeing a soldering gun of the transformer type having a fuse, but perhaps they do?

Either it is poor design or that is a knockoff Weller, just checked both my cheapie soldering stations one circuit specialist and a Bakon from banggood and they both have fuses soldered to boards,so the Pace unit has a fuse drawer built into the IEC socket which not only has the fuse but also holds a spare but of course thats a lot more money.

For the typical small glass tube slow blow fuse form factor, isn't a 240V/1A fuse the exact same thing as a 120V/2A fuse? It's an I2R device, V does not matter much (within reason).

I was of course writing this regarding the isolation voltage after it blew - with respect to arcs/transients and general safety aspects as Dave points out in his multimeter teardowns when it comes to CAT ratings. Even though this soldering station is not CAT rated, transient overvoltage does exist, probably damage the transformer directly (a fuse wont help with that), but any additional part needs to be able to handle it?

The nominal voltage rating on the fuse is given for isolation, not in relation to it´s current carrying characteristics. Obviously that´s not an "operating voltage" which it is supposed to permanently drop, it is a fuse - a safety switch and that is it´s isolation voltage. Come on!

The discussion is getting very abstract and theoretical. I´d say there is no right or wrong way to prepare a device for this, the scenario was not a use case in the first place, the risks stay with the party that imported it to the jurisdiction. Questions around device protection usually run down to what statistically is likely to the general safety - not the most extreme outliers.

Of course a dropped neutral that connected to the other phase can happen, but that would also mean you try to solder in the dark and the beer gets warm.

Of course a dropped neutral that connected to the other phase can happen, but that would also mean you try to solder in the dark and the beer gets warm.

You've got your soldering iron on, plugged into a split outlet. You plug your new reflow oven to the other socket and turn it on. There's a bad connection on the outlet's neutral that gets worse when you dump 1500W through it and it opens.Know what you speak of.

Split outlets and the code for them are a new-to-me concept, as i am on a different continent. So excuse the dumb question: isn´t a double neutral feed required for those, as the gauge needs to match the cross sectional area for the live wire anyway? I don´t know if cable with two gauges in one sheathing would be usual.. hence two live/two neutral would make sense.

But i think i get what you address: a floating neutral on a per outlet basis... a lower impedance load would be in series with the device at double (180° split) the operating voltage, shifting the voltage drop according to their impedance (guess 0.8A/12.5A nominal=224,6V/15,4V), while the current for both is drawn through the soldering stations feed line/transformer/switch/fuse*. A fuse could help with that, but it heavily depends which device and which kind of device is switched on first.

OTOH: If the other, unkown device had a higher impedance, the soldering station would have undervoltage, lower current.

House installation and devices are usually handled separate, as the device manufacturer can only cover his part, not the rest of the installation and vice versa.

Interestingly, as Dave suggested, the EN 60335-1 doesn't *require* the use of any fuse or even any specific protection measures at the primary side. They may be used as a means of being compliant, but are not strictly required.

The fault conditions that are tested are ALL simulated while the device is powered at the *rated voltage*, except two. There is basically one test in which the input voltage is lowered until the device stops functioning, then it's raised again to the rated voltage - and the device should be back to an operating state (probably to simulate power cuts). The other is a surge test, but as the surge pulses are relatively short, the transformer probably takes the abuse gracefully, and the protections at the secondary side are sufficient...

To get away with not doing anything more, they probably selected a transformer that is already tested compliant to some UL standard, and documented the device's fabrication process. And there you go.

This is still dubious engineering practise, but the device is most likely compliant to the required standards indeed...

Split outlets and the code for them are a new-to-me concept, as i am on a different continent. So excuse the dumb question: isn´t a double neutral feed required for those, as the gauge needs to match the cross sectional area for the live wire anyway?

As you said, the two live wires would be 180 degrees out of phase, so when both are in use, the current in the neutral would subtract, not add. A single neutral is all that's required, and it is the same gauge wire as the two live wires.

The electrical code in the US has become more strict in this in recent years. They call this a "multi-wire branch circuit," and you used to be able to legally run it off two separate breakers in the panel, of course making sure that they were on opposite legs of the incoming service. But now those breakers are required to have at least a handle tie, so one can not be shut off without also shutting off the other.

Personally, I still like the idea of using multi-wire branch circuits, for conservation of resources and operation of the circuits with lower voltage drop. Particularly in a commercial setting with wires running through conduit, if you follow the code requirements on de-rating ampacity when you have multiple conductors in the same conduit, you can really save a lot of materials if you use multi-wire branch circuits. For instance, on a 3-phase system, 3 circuits can share one neutral and only count as 3 current-carrying conductors (because the neutral current cancels out, at least when driving linear loads that don't introduce harmonics). But if you ran each of the three circuits with its own neutral, you have to count it as 6 current-carrying conductors, and then you have to increase the size of conductor because you have to de-rate the amps rating when you have so many conductors in one conduit. NEC Table 310.15(B)(3)(a). Then you have to increase the conduit size because the conductors are bigger.

The Code has been evolving towards prohibition of multi-wire branch circuits with shared neutrals. Many electricians and electrical system designers now like running each circuit with its own neutral for greater reliability (not having to shut off multiple circuits to work on one) and less danger in case of an open neutral.

I got very expensive station when working in telephone company, it is 25 year old...actually it never was at work - I was using it only at home : ) Mains fuse is locatedat front panel there, never looked inside or opening the fuse.https://commons.wikimedia.org/wiki/File:Loetstation_Weller_WTCP-S.jpgI had similar blue alpha Rosin Core solder wire reel... sweet smell.

But my hi-tech new soldering station doesn't have any fuse, even protective sleevesare loose on mains connection. "Hakko'd" together from UPS transformer, clone frontpanel and HAKD 907 handle.I don't know who to blame...: )))

Soldering guns generate a many kV spike at the tip on trigger switch off. Don't use them on electronics! KILLER

How is that possible? The secondary that forms the tip is like a single loop buss bar, a dead short. When I was a young kid, the Weller gun was all I had, but granted I was only soldering wire in tube circuits and transistors, nothing static sensitive. In all those years, I don’t think I ever saw a spark off that tip.

Capacitive coupling of the back-EMF spike from breaking the primary circuit, to the secondary is how. However its pretty easy to mitigate. Simply connect the inner end of the primary to neutral, not to the switch, to minimise the coupling, and put a snubber across the switch.